Math Mammoth Add & Subtract 2-B is a continuation to the book Math Mammoth Add & Subtract
2-A. The goal of this book is to study addition and subtraction within 0-100, both mentally and in
columns, especially concentrating on regrouping in addition (carrying) and in subtraction (borrowing).

The PDF version of this book is enabled for annotation. This means that if you prefer, your student can fill it in on the computer, using the typewriter and drawing tools in Adobe Reader version 9 or greater.

Mental math

Mental math is important because it builds number sense. This book includes many lessons that practice
mental math. For example, the child practices adding and subtracting two-digit numbers when one of the
numbers is a whole ten (problems such as 30 + 14, or 66 − 20).

Also studied are problems such as 36 + 8 or 45 + 9. These problems use the idea of going over ten as in
problems 6 + 8 and 5 + 9. The child knows that 6 + 8 fills the first ten and is four more than the ten.
He/she will learn to use that fact when adding 36 + 8. The sum 36 + 8 fills the next whole ten (40), and is
four more than that, or 44.

Regrouping in tens

Simultaneously with this, the child learns adding two-digit numbers in columns, and regrouping with tens,
or "carrying," which is illustrated and explained in detail with the help of visual models. These visual
models take the place of base-ten blocks or other manipulatives. You are welcome to use manipulatives to
get the idea across, if you prefer. The main concept to understand is that 10 ones are regrouped to form a
new ten, and this new ten is written using a little "1" in the tens column.

Regrouping in subtraction

The next lessons teach subtracting in columns. First we only deal with the easy problems where you don't
need to regroup (borrow). Then the following lessons practice in detail the process of regrouping or
borrowing. You can use either term with your child, or even choose not to use either if you feel it is
confusing. You can alternatively use the phrase "breaking a ten into ten ones."

First, the lesson Regrouping practices breaking down a ten into ten ones because we cannot subtract from
the ones. It is crucial that the child understands what happens here. Otherwise, he/she might end up only
memorizing the procedure, and will probably at some point misremember how it was done. That is why
this lesson deals with the regrouping process in detail with plenty of visual exercises.

If you notice that the child does not understand the concept of regrouping, he/she may need more practice
with concrete manipulatives or visual exercises before proceeding.

More mental math

After learning regrouping, we practice mental subtraction in three separate lessons. One of them expounds
on several methods for mental subtracting. Another is about Euclid's game—a fun game that also
practices subtraction of two-digit numbers.

The video below shows a similar idea as to what is in the book about regrouping (borrowing).

How and where to order

You can buy Math Mammoth books at:

Here at MathMammoth.com website — simply use the "Add to cart" buttons you see on the product pages.

CurrClick.com carries all Blue, Golden, and Light Blue series books as downloads. They accept credit cards and Paypal. You will be able to download the products immediately upon the purchase, and also return to your account at CurrClick to redownload.

Lulu offers printed copies for the Blue, Golden, and Light Blue series books.

By purchasing any of the books, permission IS granted for the teacher (or parent) to reproduce this material to be used with his/her students in a teaching situation; not for commercial resale. However, you are not permitted to share the material with another teacher.

In other words, you are permitted to make copies for the students/children you are teaching, but not for other teachers' usage.

Math Mammoth books are PDF files. You will need Adobe Reader to view them, including if you use a Mac or Linux. You can try other PDF viewers, but they seem to either omit or mess up some of the images.

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